13.4.txt

13.4  Be True in the Eyes of Ruby

In Ruby, there are two values that evaluate to false in a Boolean expression. One of them is, of course, false. The other is nil. Every other value is evaluated as true. Even 0:

puts "0 evals to true" if 0

RSpec’s be_true and be_false matchers can be used to specify methods that  should  return  values  that  Ruby  will  evaluate  as  true  or  false,  as opposed to the actual values true and false:

true.should be_true
0.should be_true
"this".should be_true

false.should be_false 
nil.should be_false

For the rare cases in which we care that methods return the values true or false, we can use the equal( ) matcher:

true.should equal(true)
false.should equal(false)

Up until now we’ve been discussing expectations about the state of an object.  The  object  should  be_in_some_state.  But  what  about  when  the state we’re interested in is not in the object itself but in an object that it owns?